A composite phase change material for improving the freeze–thaw resistance performance of cement mortars

Abstract

Over 50% of engineering structures on earth seasonally suffer from long-term freeze–thaw cycles, which significantly decreases their durability. Cement-based materials (CBMs) are most widely used in civil engineering and often damaged by cyclic freeze–thaw action, so their service lives fall below design expectations. To improve the freeze–thaw resistance performance of CBMs, we chose n-tetradecane encapsulated in expanded graphite as a phase change material (PCM) to produce a new composite phase change cement mortar (PCCM). Four mass ratios of the PCM to cement were selected to mix with cement and fine aggregates. The key physical and chemical properties of the components in the new PCCM are tested to prove their material functions. Then, the physical and mechanical performance of the new PCCMs were also tested under different numbers of freeze–thaw cycles. The monitoring results show that the new composite PCCMs designed in this study all have excellent freeze–thaw resistance performance, according to which an optimal content of the PCM for the PCCMs was pointed out. The PCCMs’ ability to reduce freeze–thaw cycles was sufficiently analyzed by a numerical simulation of the heat transfer. The composite method and experimental results of the new PCCMs proposed in this study provide an important reference for industrial production and are also helpful for understanding the freeze–thaw mechanism of cement mortars.